A conventional MOS transistor generally includes a semiconductor substrate, such as silicon, having a gate structure or gate stack formed thereover. The gate structure comprises a conductive gate electrode overlying a thin gate dielectric. The gate electrode typically includes polysilicon and the gate dielectric an oxide based material. Source and drain regions are formed in the substrate substantially aligned with the gate structure. The source and drain regions are generally formed by applying a dopant to the select regions of the substrate. A channel is defined within the substrate under the gate structure between the source and drain regions.
A voltage applied to the gate electrode induces an electric field across the channel of the MOS transistor, and the amount of current that flows through the channel is directly proportional to an activation level of the source and drain regions. Thus, the higher the activation level of the source and drain regions, the more current can flow and the faster a circuit can perform wherein such a MOS transistor is incorporated. Phosphorous is a dopant that causes source and drain regions to have a high activation level as compared to conventional source/drain dopants, such as arsenic, for example. However, phosphorus has a high diffusity which can lead to non-abrupt junctions. Non-abrupt junctions can be detrimental to the performance of the transistor by adversely affecting channel characteristics, injection velocity, carrier mobility and/or drive current.
It would thus be advantageous to have a phosphorus doped transistor wherein diffusity is substantially mitigated.